Improvement in pneumatic signaling apparatus



UNTTED STATES WILLIAM E. PRALL, OF WASHINGTON, DISTRICT OF COLUMBIA.

IMPROVEMENT IN PNEUMATIC SlGNALlNG APPARATUS.

Specification forming part of Letters Patent No. l 7,2,934, dated February 1, 1876; application iiled January 15, 1876.

To all whom it may concern:

Be it known that I, WILLIAM E. PRAL'L, of Washington, District of Columbia, have invented an Improved Double-Acting Danger-Signal for Railway-Crossings, of which the following is a specification:

This invention has forits object the movement ofa railroad-signal, by the ad mission to its operative piston or diaphragm of compressed air from si gnal supply-pipes, stretching in opposite directions therefrom, so that it shall be operated by trains coming in either direction; and it consists in the combination of a double acting valve with the two signal supplypipes and the piston-cylinder of the signal, so as that, when the valve is thrown to open communication between either of the pipes and -the cylinder, the communication between the cylinder and the other pipe shall be closed. v

In the accompanying drawings, Figure 1 is a sectional view of an air-piston carryinga rack engaging a pinion to operate a signal gate or guard for a railway-crossing, illustrating the combination of my invention therewith; Fig. 2 is an elevation ofthe same vdevice; and'Fig. 3 a detached view, illustrating the use of a ball-valve'in the foregoing combination. l

A is a cylinder inclosing a piston, B, which carries a rack, C, engaging the pinion D of a shaft, X, bywhich a gate for guarding the road-crossings of railways may be operated. The lower head E of the cylinder is formed with a projecting tubular T-piece, to form a valve-chest for a valve, F. G G' are signal supply-pipes communicating' with this valvechest on opposite sides of the valve F. The valve F is secured in place by means of a cap, H, screwing into thelbottom of .the valve-chest. vThis valve F may consist of a -iiap-plate, as illustrated in Fig. 1, or of a ball, as shown in Fig. 3, or other equivalent device, which may serve to cover and close alternately the two ports communicatingwith' the signal-pipes G G'.

The interior of the valve-chestcommunicates freely with the cylinder, so that when the valve covers the port of one of the supplypipes G, the other supply-pipe, G', shall have free communication with the piston-chamber, and vice versa. The valve itself is so pivoted, as in Fig. 1, or seated, as in Fig. 3, as

that it will not move away from contact with either port, except when forced away therefrom by a pressure from within the supplypipe closed thereby. The valve-chest may be formed independently of the head E of the cylinder, and be separately secured thereto.

In the operation of this apparatus, when a train approaches from the directionfor instance-0f the pipe G', and, by a movement of the supply-commutator at the far extremity of said pipe, admits a charge of compressed air thereto, as described in the Letters Patent for pneumatic railway-signals heretofore granted to me, the air will force the valvev F from its seat against the port at the mouth of the opposite pipe G and close it, and will then pass into the cylinder A and force up its piston B, as shown in Fig. 1.

If, while the valve F remains in this position, the exhaust-comniutator valve of said pipe G' he thrown open, the air will escape from the'cylinder through the port of the pipe G', and the signal be reversed. If, however, while the air is exhausting from the cylinder and the signal is being reversed, a train approaches from the opposite direction, and a charge of air is admitted thereby to the pipe G, the pressure of the air against the valve F will throw it over, cause it to close the port ot' the exhausting-pipe G', and, by refilling the cylinder A, will arrest the downward movement ofthe piston and force it up again.

Thus, although the exhaust of air will continue from the pipe G', its escape from the cylinder A in this direction is prevented, and the signal will remain displayed until the exhaust is opened in the opposite pipe G. Hence it is evident that, by this invention, the one signal-piston B will be operated by an admission of air from either pipe, even after the exhaust in the one pipe or the other has been opened, so that the signal will thus invariably be thrown to indicate danger upon the. approach of a train from either direction, in*

dependently of the opening oi' the exhaust PATENT rtrcn;`

y the passage of a previous train, and will independent air-supply pipes and 'the pistouemain in position until the air is exhausted chamber of a. pneumatic signal, substantially vom both pipes by the passage of both trains as and for the purpose herein set forth. eyond the danger-point.

A diaphragm may be substituted for the p W. E. PRALL. iston as its equivalent. Witnesses:

I claim as my invention- WM. E. KNOWLES,

A double-acting valve, combined with two DAVID A. BURR. 

